Accept previousCycles as array

lib/sympto/pre-ovulatory.js

@@ -1,13 +1,20 @@
 import { LocalDate } from "js-joda"
 
-export default function(cycle) {
+export default function(cycle, previousCycles) {
+  // TODO handle no previous cycles
+  let preOvuPhaseLength = 5
+
+  //TODO make sure it handles weird cases like fhm < 9
+  const minus8DayRuleResult = apply8DayRule(previousCycles)
+  if (minus8DayRuleResult) preOvuPhaseLength = minus8DayRuleResult
+
   const startDate = LocalDate.parse(cycle[0].date)
-  const fiveDayEndDate = startDate.plusDays(4).toString()
-  const fiveDayRuleDays = cycle.slice(0, 5).filter(d => d.date <= fiveDayEndDate)
-  const preOvulatoryDays = getDaysUntilFertileMucus(fiveDayRuleDays)
+  const preOvuPhaseEndDate = startDate.plusDays(preOvuPhaseLength - 1).toString()
+  const maybePreOvuDays = cycle.slice(0, 5).filter(d => d.date <= preOvuPhaseEndDate)
+  const preOvulatoryDays = getDaysUntilFertileMucus(maybePreOvuDays)
   let endDate
-  if (preOvulatoryDays.length === fiveDayRuleDays.length) {
-    endDate = fiveDayEndDate
+  if (preOvulatoryDays.length === maybePreOvuDays.length) {
+    endDate = preOvuPhaseEndDate
   } else {
     endDate = preOvulatoryDays[preOvulatoryDays.length - 1].date
   }
@@ -29,4 +36,6 @@ function getDaysUntilFertileMucus(days) {
     return days.slice(0, firstFertileMucusDayIndex)
   }
   return days
-}
+}
+
+function apply8DayRule() {}